Supposedly according to the science that rolling resistance on a road bike is at its least with a 25mm tire, going one size down or one size up from that and the resistance increases a tad, and the pros are recognizing that and all, except for one, of the pro peloton is riding on 25mm tires, the only exception that I could find was running 26mm. Having said that I'm confused about the following, but I also use still do this with my tires (not with Conti though), why Conti Attack tires still offer 23mm for the front and 25mm for the rear, according to Conti the front needs to be a bit more aero in because it's the first to hit the air stream, but the rear is protected by the seattube and thus a wider tire is better; I'm not sure what to think of all of this, I've done it this way because years ago I was told that's the best way after running 23's all around for many years, now we're being told 25 (maybe 26) all around is the better way, I simply don't know. For years they said eggs were good for you, then for years they said eggs were bad for you, now they're back to saying eggs are good for you, does anybody really know for sure if eggs are good or bad for you? Does anyone really know for sure that running 23 in the front and 25 in the rear instead of 23 or 25 all around is good or bad? I can see at sometime in the future that the science takes us back to 23 all around or a mixture of sizes if eggs is any example. I do like the fact that when the larger rear tire wears out the front is usually also darn near worn out instead of having the front only half worn as you do with using the same size all around, so when my tires are worn I just buy a pair and put them on.